From an examination of Tables I to III, and Figs. 1 to 4 and the consideration of various observations, the following facts are evident. A virulent pneumococcus on being transformed into its-avirulent form consumes many times more oxygen than the parent organism; but this gain of activity is a temporary property. After a time it degenerates into a form which consumes very much less oxygen than either the virulent or the recently derived avirulent form. In a comparative study of the metabolic functions, and oxidation products of various virulent and avirulent pneumococci, these phenomena should receive consideration. The change that takes place in the structure of the enzyme responsible for carbohydrate biosynthesis during the shift from the virulent to the avirulent form may be associated with the changes in the enzyme structure already demonstrated in connection with these metabolic studies.